The new approach of targeted cancer therapy has been received well, but an underlying theme needs to be addressed. Many of the proteins that are targeted for cancer therapy also have a major role in the heart. Our laboratory's long-term goals are to better understand erbB2 and HSP90 function in the heart, identify patients at risk for cardiac injury from cancer therapy, and develop new treatment strategies that can effectively treat cancer while also protecting the heart from the cancer therapeutic agents. We hypothesize that erbB2 is induced in the heart by oxidative stress, and that it also has a central role in protecting the heart from oxidative stress (including stress induced by doxorubicin therapy). Furthermore, we hypothesize that the chaperone HSP90 cooperates in this cellular protection by stabilizing the erbB2 protein in heart cells. Aim 1: Determine the role of oxidative stress and associated cell signaling to induce cardioprotection through erbB2 or HSP90 (protein or mRNA) and the role of NF- using the following oxidative stress models: 1) H2O2, xanthine/xanthine oxidase and glutathione depletion in rat cardiomyocytes and in vivo glutathione depletion 2) diabetes cardiomyopathy, and 3) redox modulation with resveratrol or geranylgeranylacetone to prevent doxorubicin toxicity. Additionally, we will determine the role of free radical scavengers on erbB2 expression and the role of erbB2 pathway inhibition on cellular protection during oxidative stress. Aim 2: Determine whether the cardioprotective role of erbB2 is due to a reduction of cardiac oxidative stress. Here we aim to assess whether: 1) erbB2 pathway inhibition in cardiomyocytes (through anti-erbB2 or siRNA) results in increased oxidative stress and dysfunction in the mitochondria, and thus increased sensitivity to doxorubicin, 2) lapatinib induces cardiac oxidative stress and cell death in vivo, with or without doxorubicin therapy compared to cancer xenografts, 3) transgenic cardiac-specific over-expression of erbB2 protects from oxidative stress and mitochondrial dysfunction in two models of oxidative stress (doxorubicin-induced cardiomyopathy and streptozotocin-induced diabetes cardiomyopathy). Aim 3: Determine the cellular protective role of HSP90 as a chaperone of erbB2 protein in the heart. Here we aim to assess whether: 1) cardiac-specific over-expression of HSP90 in a transgenic mouse model reduces heart failure, cell death and oxidative stress via stabilization of erbB2 in two models: doxorubicin-induced heart toxicity or streptozotocin-induced diabetes cardiomyopathy; 2) inhibiting HSP90 protein expression or function increases cardiomyocyte death during doxorubicin therapy in vitro with siRNA or in vivo with 17AAG in mice with cancer xenografts, and 3) HSP90 inhibitor (17AAG) affects cardiac erbB2 levels in isolated hearts and inhibits heart function and mitochondrial function. The public health significance of this project is that we aim to protect patients from severe cardiotoxic effects of anti-cancer drugs, which in many cases, limits the use of otherwise effective therapies. The public health significance of this project is that we aim to protect patients from severe cardiotoxic effects of anti-cancer drugs, which in many cases, limits the use of otherwise effective therapies.